IOL implants have been used for many years in aphakic (i.e. absent lens) eyes as replacements for diseased natural crystalline lenses that have been surgically removed from the eyes. Many different IOL designs have been developed over past years and proven successful for use in aphakic eyes. Successful IOL designs to date primarily include an optic portion with supports therefore, called haptics, connected to and surrounding at least part of the optic portion. The haptic portions of an IOL are designed to support the optic portion of the IOL in the lens capsule, anterior chamber or posterior chamber of an eye.
Commercially successful IOLs have been made from a variety of biocompatible materials, ranging from more rigid materials such as polymethylmethacrylate (PMMA) to softer, more flexible materials capable of being folded or compressed such as silicones, certain acrylics, and hydrogels. Haptic portions of the IOLs have been formed separately from the optic portion and later connected thereto through processes such as heat, physical staking and/or chemical bonding. Haptics have also been formed as an integral part of the optic portion in what is commonly referred to as “single-piece” IOLs.
Softer, more flexible IOLs have gained in popularity in recent years due to their ability to be compressed, folded, rolled or otherwise deformed. Such softer IOLs may be deformed prior to insertion thereof through an incision in the cornea of an eye. Following insertion of the IOL in an eye, the IOL returns to its original pre-deformed shape due to the memory characteristics of the soft material. Softer, more flexible IOLs as just described may be implanted into an eye through an incision that is much smaller, i.e., 2.8 to 3.2 mm, than that necessary for more rigid IOLs, i.e., 4.8 to 6.0 mm. A larger incision is necessary for more rigid IOLs because the lens must be inserted through an incision in the cornea slightly larger than the diameter of the inflexible IOL optic portion. Accordingly, more rigid IOLs have become less popular in the market since larger incisions have been found to be associated with an increased incidence of postoperative complications, such as induced astigmatism.
After IOL implantation, both softer and more rigid IOLs are subject to compressive forces exerted on the outer edges thereof from natural brain-induced contraction and relaxation of the ciliary muscle and increases and decreases in vitreous pressure. Compressive forces of this kind are useful in a phakic eye for focusing the eye at various distances. Most commercially successful IOL designs for use in aphakic eyes have single focus optic portions that are fixed and focus the eye at only a certain fixed distance. Such single focus IOLs require the wearing of glasses to change the focus of the eye few bifocal IOLs have been introduced to the commercial market but suffer from the disadvantage that each bifocal image represents only about forty percent of the available light and the remaining twenty percent of the light is lost to scatter, which provides lessened visual acuity.
Because of the noted shortcomings of current IOL designs, there is a need for IOLs designed to provide multifocal visual imaging in aphakic eyes without the aid of eyeglasses.
Current multifocal IOLs are based on integrating a few optical zones within the IOL surface to create a limited number of focal points on the cornea, e.g. U.S. Pat. Nos. 6,695,880 and 6,089,711. Each focal point or zone offers corrected vision at a specific distance (near, intermediate, and far). Accommodating IOLs are designed to simulate the performance of the healthy natural lens when the focus shifts from far to near or vice versa by allowing the IOL to move within the eye. Neither type of lenses performs satisfactorily.
The present invention is based on the novel concept that making an IOL with a true infinite refractive index gradient (IRIG) would provide patients with improved near, far and intermediate vision. In fact, the human natural lens has a true IRIG that is responsible for accommodation, depth of field perception and contrast sensitivity. More importantly, the contribution of IRIG to the lens power of the natural lens decreases significantly with age at a rate of 0.286±0.067 diopter per year (ref). This change accounts almost entirely for the estimated overall loss of accommodation responsible for presbyopia and loss of contrast sensitivity. An IOL similar in IRIG to a healthy human natural lens would restore accommodation and adequate vision to cataract patients.